Method of DCR operation in a broadband wireless communication system

ABSTRACT

The present invention relates to a broadband wireless access system, and more particularly, to a method for a mobile station to save power for prescribed duration without performing a paging procedure and apparatus therefor. According to one embodiment of the invention, a method of operating a DCR (deregistration with content retention) mode of a mobile station in a broadband wireless access system includes the steps of transmitting a registration request (AAI_REG-REQ) message to a base station and receiving a registration response (AAI_REG-RSP) message including an identifier for identifying the mobile station in association with connection information (AMS context) of the mobile station in a network including a base station from the base station.

The present application is a 37 C.F.R. §1.53(b) continuation of U.S.patent application Ser. No. 12/786,135 filed May 24, 2010 now U.S. Pat.No. 8,259,681, which claims priority on Korean Patent Application No.10-2010-0020740, filed Mar. 9, 2010, and which claims priority on U.S.Provisional Application Ser. Nos. 61/180,883, filed on May 24, 2009,61/238,197, filed on Aug. 30, 2009, 61/294,098, filed on Jan. 11, 2010,and 61/238,640, filed on Aug. 31, 2009. The entire contents of all ofthe above applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a broadband wireless access system, andmore particularly, to a method for a mobile station to save power forprescribed duration without performing a paging procedure and apparatustherefor.

2. Discussion of the Related Art

In the following description, an idle mode of a mobile station and apaging group are schematically explained.

First of all, when a mobile station moves in a radio link environmentconstructed with multiple base stations, an idle mode is an operation ofsupporting DL (downlink) broadcast traffic reception to be periodicallyperformed without registration with a specific base station.

When a mobile station fails to receive traffic from a base station forpredetermined duration, it is able to enter an idle mode for powersaving. Having entered the idle mode, the mobile station receives abroadcast message (e.g., a paging message) sent by the base station inan available interval and is then able to determine whether to enter anormal mode or stay in the idle mode. Moreover, the mobile station inthe idle mode performs a location update to inform a paging controllerof its location.

An idle mode gives a benefit to a mobile station in a manner ofeliminating a request for activation associated with a handover andgeneral management requests. The idle mode puts limitation on mobilestation activity in a manner of enabling a mobile station to perform ascan in a discrete cycle only. Therefore, the idle mode saves power andoperational resources used by the mobile station.

An idle mode provides a simple and appropriate method of informing amobile station of pending downlink traffic and removes a radio interfaceand network handover (HO) traffic from an inactive mobile station,thereby giving benefits to a network and a base station.

Meanwhile, a paging means a function of obtaining a location (e.g., aprescribed base station, a prescribed switching center, etc.) of amobile station corresponding to an incoming signal occurrence in mobilecommunication. A plurality of base stations (BSs) supporting the idlemode can configure a paging area by belonging to a specific paginggroup.

In this case, the paging group indicates a logical group. The object ofthe paging group is to provide an adjacent range area that can be pagedin downlink (DL) if there is a traffic targeting a mobile station (MS).Preferably, the paging group is large enough to enable a specific mobilestation to exist within the same paging group for the most of time andis also small enough to enable a paging load to maintain an appropriatelevel.

A paging group can include at least one base station. And, one basestation can be included in at least one or more paging groups. A paginggroup is defined by a management system. A paging group is able to use apaging group-action backbone network message. A paging controllermanages a list of mobile stations in idle mode using a paging-announcemessage that is one of backbone network messages. And, the pagingcontroller is able to manage initial paging of all base stationsbelonging to a paging group.

In order to increase a rate of successful paging, a mobile station isable to perform a location update procedure. In this case, a locationupdate is an action of a mobile station to increase a hit rate of pagingperformed on a mobile station having entered an idle mode and indicatesa procedure for a mobile station to report a newly entered location orregion in moving into a new region. This location update procedure canbe performed in a manner that a mobile station and a base stationexchange a ranging request (RNG-REQ) message and a ranging response(RNG-RSP) message with each other.

In the following description, one example for a procedure for a mobilestation to enter an idle mode and operate in the general IEEE 802.16system is explained with reference to FIG. 1.

Referring to FIG. 1, first of all, a mobile station is able to send aderegistration request (hereinafter abbreviated DREG-REQ) message to aserving base station to enter an idle mode from a normal mode [S101].

Having received the DREG-REQ message, the serving base station canexchange information on the mobile station and information on itselfwith a paging controller. IN particular, the serving base station isable to inform the paging controller of a mobile station identifier ofthe mobile station entering an idle mode and a corresponding servingbase station identifier. And, the paging controller is able to informthe serving base station of a paging group ID (PGID) or a pagingcontroller ID (PCID). The paging group ID or the paging controller ID isusable in transmitting and receiving a paging message [S102].

Subsequently, the serving base station is able to transmit aderegistration command (hereinafter abbreviated DREG-CMD) to the mobilestation. The serving base station is able to send a deregistrationcommand (MOB_DREG-CMD) message to the mobile station in response to thederegistration request message. In this case, the deregistration commandmessage can contain paging information therein. And, the paginginformation can include such a parameter as a paging cycle, a pagingoffset, a paging listen interval and the like. Moreover, thederegistration command message can further contain a paging controllerID and a paging group ID [S103].

Having received the DREG-CMD message from the serving base station, themobile station checks that the idle mode entry request has beensuccessfully granted and is then able to enter the idle mode. Based onthe paging information carried on the MOB_DREG-CMD message, the mobilestation is able to receive the paging message. In particular, the mobilestation is able to monitor a radio channel during the paging listeninterval to check whether there is a paging message to be delivered toitself. For the rest of time, the mobile station operates in a sleepmode or a radio turn-of mode to save power consumption [S104].

A call for the mobile station or an external packet can be inputted tothe paging controller [S105].

The paging controller can correspondingly perform a paging procedure fordetecting a mobile station. In doing so, the paging controller is ableto deliver a paging announcement message to all the base stations withina paging group [S106].

Subsequently, each of the base stations having received the pagingannouncement message within the paging group can broadcast a pagingadvertisement (MOB_PAG-ADV) message to every mobile station managed bythe corresponding base station [S107].

Having received the paging advertisement message from the serving basestation, the mobile station checks the received message. If the mobilestation is paged, the mobile station enters a normal mode and is thenbale to perform communication with the serving base station [S108,S109].

However, in the general IEEE 802.16 based wireless communication system,a mobile station has to enter an idle mode to save power despite that apaging procedure is unnecessary. So, paging relevant information isunnecessarily allocated to the mobile station. Thus, although the mobilestation in the idle mode needs not to receive a paging message, themobile station should wake up to cope with a paging interval.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method of DCRoperation in a broadband wireless communication system thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a method for a mobilestation to save power for prescribed duration without performing apaging procedure and apparatus therefore, by which the power can beefficiently saved.

Another object of the present invention is to provide a method ofperforming a network re-entry in a mode for power saving and apparatustherefore, by which the network re-entry can be efficiently performed.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod of operating a DCR (deregistration with content retention) modeof a mobile station in a broadband wireless access system, according tothe present invention includes the steps of sending a registrationrequest (AAI_REG-REQ) message to a base station and receiving aregistration response (AAI_REG-RSP) message including an identifier foridentifying the mobile station in association with connectioninformation (AMS context) of the mobile station in a network including abase station from the base station.

Preferably, the identifier is a context retention identifier (CRID).

More preferably, the registration response message is received when anetwork entry is performed on the base station or a zone switch from aregion supporting a legacy mobile station of the base station to anotherregion supporting an advanced mobile station further advanced than thelegacy mobile station is performed.

In this case, the method further includes the steps of sending a firstmessage including a first code indicating an entry request at the DCRmode to the base station, receiving a second message including a secondcode indicating whether to grant the entry request from the basestation, and if the second code is set to a value indicating a grant ofthe entry request, operating in the DCR mode while a preset timer isvalid.

Moreover, the first message is a deregistration request (AAI_DREG-REQ)message, the first code indicating the entry request is a deregistrationrequest code (Deregistration_Request_Code) set to 0x04, the secondmessage is a deregistration response (AAI_DREG-RSP) message, and thesecond code indicating the grant of the entry request is an action codeset to 0x08.

In another aspect of the present invention, a method of operating a DCR(deregistration with content retention) mode of a base station in abroadband wireless access system, includes the steps of receiving aregistration request (AAI_REG-REQ) message from a mobile station andsending a registration response (AAI_REG-RSP) message including anidentifier for identifying the mobile station in association withconnection information (AMS context) of the mobile station in a networkincluding the base station to the mobile station.

Preferably, the identifier is a context retention identifier (CRID).

More preferably, the registration response message is received when anetwork entry is performed on the base station or a zone switch from aregion supporting a legacy mobile station of the base station to anotherregion supporting an advanced mobile station further advanced than thelegacy mobile station is performed.

In this case, the method further includes the steps of receiving a firstmessage including a first code indicating an entry request at the DCRmode from the mobile station, determining whether to grant the entryrequest, if the entry request is granted, delivering a context of themobile station to a prescribed network entity, and sending a secondmessage including a second code indicating a grant of the entry requestto the mobile station.

Moreover, the first message is a deregistration request (AAI_DREG-REQ)message, the first code indicating the entry request is a deregistrationrequest code (Deregistration_Request_Code) set to 0x04, the secondmessage is a deregistration response (AAI_DREG-RSP) message, and thesecond code indicating the grant of the entry request is an action codeset to 0x08.

In another aspect of the present invention, a mobile station, whichoperates in a broadband wireless access system, includes a processor anda radio communication (RF) module configured to transceive a radiosignal externally under the control of the processor. In this case, theprocessor controls the wireless communication module to send aregistration request (AAI_REG-REQ) message to a base station and toobtain an identifier for identifying the mobile station in associationwith connection information (AMS context) of the mobile station in anetwork including a base station via a registration response(AAI_REG-RSP) message received from the base station in response to theregistration request message.

Preferably, the identifier is a context retention identifier (CRID).

More preferably, the registration response message is received when anetwork entry is performed on the base station or a zone switch from aregion supporting a legacy mobile station of the base station to anotherregion supporting an advanced mobile station further advanced than thelegacy mobile station is performed.

In this case, the processor controls the wireless communication unit tosend a first message including a first code indicating an entry requestat the DCR mode to the base station. If a second message including asecond code indicating whether to grant the entry request is receivedfrom the base station and if the second code is set to a valueindicating a grant of the entry request, the processor controls tooperate in the DCR mode while a preset timer is valid.

Moreover, the first message is a deregistration request (AAI_DREG-REQ)message, the first code indicating the entry request is a deregistrationrequest code (Deregistration_Request_Code) set to 0x04, the secondmessage is a deregistration response (AAI_DREG-RSP) message, and thesecond code indicating the grant of the entry request is an action codeset to 0x08.

Accordingly, the present invention provides the following effects and/oradvantages.

First of all, according to embodiments of the present invention, amobile station is able to save power for a prescribed duration withoutperforming a paging procedure.

Secondly, the present invention enables information for a quick networkre-entry to be kept by a network entity, thereby performing a networkre-entry efficiently.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram of one example for a procedure for a mobile stationto enter an idle mode and operate in a general IEEE 802.16 system;

FIG. 2 is a diagram of one example for a DCR mode operation process of amobile station according to one embodiment of the present invention;

FIG. 3 is a diagram of one example for an operational process for amobile station to enter a DCR mode from an idle mode according to oneembodiment of the present invention;

FIG. 4 is a diagram of one example for an operational process for amobile station to enter an idle mode from a DCR mode according to oneembodiment of the present invention;

FIG. 5 is a diagram of one example for an operating process for a mobilestation operating in DCR mode to perform a network re-entry according toanother embodiment of the present invention;

FIG. 6 is a diagram of another example for an operating process for amobile station operating in DCR mode to perform a network re-entryaccording to another embodiment of the present invention;

FIG. 7 is a diagram of one example for a unified ranging channelstructure;

FIG. 8 is a diagram of a further example for an operating process for amobile station operating in DCR mode to perform a network re-entryaccording to another embodiment of the present invention; and

FIG. 9 is a block diagram of one example for structures of transmittingand receiving sides according to another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The present invention relates to a wireless access system. Referencewill now be made in detail to a method of an efficient DCR modeoperation according to various embodiments of the present invention,examples of which are illustrated in the accompanying drawings.

First of all, the following embodiments correspond to combinations ofelements and features of the present invention in prescribed forms. And,it is able to consider that the respective elements or features areselective unless they are explicitly mentioned. Each of the elements orfeatures can be implemented in a form failing to be combined with otherelements or features. Moreover, it is able to implement an embodiment ofthe present invention by combining elements and/or features together inpart. A sequence of operations explained for each embodiment of thepresent invention can be modified. Some configurations or features ofone embodiment can be included in another embodiment or can besubstituted for corresponding configurations or features of anotherembodiment.

In the description of drawings, procedures or steps, which may ruin thesubstance of the present invention, are not explained. And, proceduresor steps, which can be understood by those skilled in the art, are notexplained as well.

In exemplary embodiments of the present invention, a description is madeof a data transmission and reception relationship between a BS and aMobile Station (MS). Herein, the term ‘BS’ refers to a terminal node ofa network, which communicates directly with the MS. In some cases, aspecific operation described as performed by the BS may be performed byan upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with an MS may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘eNode B (eNB)’, ‘access point’, ‘Advanced BaseStation (ABS) etc. The term ‘MS’ may be replaced with the term ‘UserEquipment (UE)’, ‘Subscriber Station (SS’), ‘Mobile Subscriber Station(MSS)’, ‘mobile terminal’, ‘Advanced Mobile Station (AMS)’, etc.

A transmitter means a node that transmits voice or data service and areceiver means a node that receives voice or data service. Hence, an MSmay be a transmitter and a BS may be a receiver, on an uplink. Likewise,the MS may be a receiver and the BS may be a transmitter, on a downlink.

Meanwhile, the MS may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, etc.

Exemplary embodiments of the present invention may be achieved byvarious means, for example, hardware, firmware, software, or acombination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present invention may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theexemplary embodiments of the present invention may be implemented in theform of a module, a procedure, a function, etc. performing theabove-described functions or operations. A software code may be storedin a memory unit and executed by a processor. The memory unit is locatedat the interior or exterior of the processor and may transmit andreceive data to and from the processor via various known means.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802 system, a 3^(rd) Generation Project Partnership (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the steps or parts, which are not described to clearlyreveal the technical idea of the present invention, in the embodimentsof the present invention may be supported by the above documents. Allterminologies used herein may be supported by at least one ofP802.16-2004, P802.16e-2005, P802.16Rev2 and p802.16m documents whichare the standards of IEEE 802.16.

In the following description, specific terminologies are provided tohelp the understanding of the present invention. And, the use of thespecific terminology can be modified into another form within the scopeof the technical idea of the present invention.

In this disclosure, the following description is made on the assumptionof IEEE 802.16 system. Specifically, a mobile station in the followingdescription is assumed as an advanced mobile station (hereinafterabbreviated AMS) that meets the specifications defined by the IEEE802.16m standard.

A DCR (deregistration with content retention) mode proposed by thepresent invention is explained as follows.

First of all, regarding the DCR mode, although a mobile station isderegistered with a network, while a resource retain time of prescribedduration is valid, its context is retained by a network entity. In thiscase, a timer for the resource retain time can be named a resourceretain timer.

While the resource retain timer is valid, a network retains informationrequired for a quick network re-entry of a mobile station. When a DCRmode is entered, a deregistration identifier (hereinafter abbreviatedDID) is allocated to a mobile station together with a paging cycle and apaging offset. In this case, to be discriminated from a DID used for anidle mode, the allocated DID is set to identify mobile stations enteringa DCR mode in a manner of setting a value of each of the paging cycleand the paging offset to 0 or allocating the DID only without allocatingpaging cycle and offset information. In this case, the allocated DID maydiffer from a mobile station identifier used in entering the idle mode.In order to identify a mobile station in DCR mode, a separate identifier(e.g., CRID: context retention identifier) different from the DID isusable. If the separate identifier different from the DID is used, theDID can be used to identify a mobile station in an idle mode only.

If the separate identifier different from the DID is used to identify amobile station in DCR mode, the identifier can be used as an identifierfor identifying a mobile station in a coverage loss state correspondingto a case that a mobile station is disconnected by deviating fromcoverage of a current base station as well as the DCR mode. In order toidentify a mobile station in DCR mode or coverage loss state, when theseparate identifier different from the DID is used, this identifier isgenerally called CRID. Yet, this name of CRID is just given forconvenience and can be replaced by another name.

Meanwhile, in a network including at least one base station, CRID can beused to identify a mobile station in association with connectioninformation (i.e., AMS context) of the mobile station. In case of anetwork entry, this CRID can be allocated to a mobile station in amanner of being contained in a registration response (AAI_REG-RSP)message in performing a zone switch from one zone (LZone), whichsupports a legacy mobile station (YMS, mobile station of IEEE 802.16especification), into another zone (MZone) that supports an AMS in theIEEE 802.16m system. When a mobile station performs a network re-entry(e.g., a case of performing a handover, a case of returning from DCRmode, a case of performing a network re-entry in coverage loss state,etc.), the CRID can be updated via a ranging response (AAI_RNG-RSP)message.

First Embodiment

According to one embodiment of the present invention, a method for amobile station to enter a DCR mode is provided.

In the following description, a method of entering a DCR mode in a statethat a mobile station is connected to a network is explained withreference to FIG. 2.

FIG. 2 is a diagram of one example for a DCR mode operation process of amobile station according to one embodiment of the present invention.

Referring to FIG. 2, while a mobile station connected to a serving basestation is normally performing a data exchange, the mobile station mayenter a DCR mode [S201].

For this, the mobile station is able to initiate the DCR mode in amanner of setting the DCR mode to a specific parameter value in aderegistration request (AAI_DREG-REQ) message and then sending themessage to the serving base station [S202].

In this case, the specific parameter preferably includes aderegistration request code (Deregistration_Request_Code) field and itsvalue can be set to 0x04.

In particular, regarding the parameter setting, a configuration of thederegistration request code transmitted via the AAI_DREG-REQ message canbe classified into two types shown in Table 1.

Table 1 partially shows one example for a deregistration request messageapplicable to embodiments of the present invention.

TABLE 1 De-registration_Request_Code (included in AAI_DREG-REQ) Value0x04 Request for AMS deregistration from serving ABS and initiation ofdeep idle mode for AMS hibernation. This mode is able to drop a packetwhen the packet (IP packet included) to AMS arrives at a network. 0x05Request for AMS deregistration from serving ABS and initiation of deepidle mode for inter-RAT HO. This mode enables a packet to be forwardedto RAT in which MS is currently operating when the packet (IP packetincluded) to AMS arrives at a network.

Referring to Table 1, in case that a deregistration request code is setto 0x04, a base station is able to drop a data packet for acorresponding mobile station. In case that a deregistration request codeis set to 0x05, a base station is able to forward a data packet to atarget RAT (radio access technology) base station. As an activityaccording to the code value 0x04 or 0x05 may vary in a network layer, itmay be necessary to discriminate a request code. Yet, in case of anormal DCR mode entry, a deregistration request code value is preferablyset to 0x04.

In this case, the mobile station is able to make a request for retain aspecific service and operation information for the purpose of DCR modemanagement. For this, the specific service or operation information,which is requested to be retained, is included as a format of DCR moderetain information element. In this case, the DCR mode retaininformation element can be equal to or different from an idle moderetain information element.

In case that the serving base station grants the DCR mode entry requestmade by the mobile station, the serving base station is able to forwardthe information retain-requested by the mobile station to a networkentity (in this case, a paging controller or an authenticator ASN GW)[S203].

Moreover, the serving base station sets an action code to a specificvalue in a deregistration response message (AAI_DREG-RSP) and sends theAAI_DREG-RSP message to the mobile station [S204].

In this case, each value of the action code included in thederegistration response message is illustrated in Table 2.

TABLE 2 Action Code (included in AAI_DREG-RSP) Value 0x00 AMS shallimmediately terminate service with the ABS and should attempt networkentry at another ABS. 0x01 AMS shall listen to the current ABS but shallnot transmit until a RES-CMD message or AAI_DREG-RSP message with actioncode 0x02 or 0x03 is received. 0x02 AMS shall listen to the current ABSbut only transmit on the basic and primary management flows. 0x03 AMSshall return to normal operation and may transmit on any of its activeconnections. 0x04 This option is valid in response to a AAI_DREG-REQmessage with De-Registration Request Code = 0x00. The AMS shallterminate current Normal Operation with the ABS. 0x05 AMS shall beginidle mode initiation: a) to signal AMS to begin idle mode in unsolicitedmanner or b) to allow AMS to transmit AMS-initiated idle mode request atthe REQ-Duration expiration 0x06 This option is valid only in responseto a AAI_DREG-REQ message with De-Registration Code 0x01: a) to rejectAMS-initiated idle mode request or b) to allow AMS to transmitAMS-initiated idle mode request at the REQ-Duration expiration 0x07 Thisoption is valid only in response to an AAI_DREG-REQ message with De-Registration Request Code 0x01 to allow AMS-initiated idle mode request0x08 This option is valid only in response to an AAI_DREG-REQ messagewith De- Registration Request Code 0x04 to allow retention of the AMS'sconnection information 0x09 This option is valid only in response to anAAI_DREG-REQ message with De- Registration Request Code 0x04 to rejectretention of the AMS's connection information.

Referring to Table 2, since the specific value corresponds to a case ofallowing the connection information retention of the mobile station forthe deregistration request code 0x04 of the mobile station, it ispreferably set to 0x08. In this case, if the mobile station attempts anetwork re-entry in the DCR mode, an identifier for identifying themobile station can be included. If the identifier is used like the DIDused for the idle mode, all paging information (i.e., a paging cycle, apaging offset, etc.) is set to ‘0’ or ‘null’. If the identifier is notincluded in the deregistration response message, it should be indicatedthat the DID included in the deregistration response message is theidentifier used in the DCR mode.

If a separate identifier different from the DID is used as theidentifier, CRID corresponding to the separate identifier can beincluded in the deregistration response message. In case that the CRIDis used, it can be allocated via a registration response message(AAI_REG-RSP) in a network entry or re-entry procedure before a DCR modeentry or via a deregistration response message. In case that the CRID isused, the CRID can be configured in a manner that a DID is combined withone or more bits indicating paging information set to 0 or that a 1- or2-bit identifier indicating whether to be used in DCR mode is added to aDID. This identifier shall be described in detail later.

A specific service or operation information, which can be retained as aDCR mode retain information element) in response to informationretention-requested by the mobile station, can be included in thederegistration response message. In this case, the DCR mode retaininformation element may be equal to or different from an idle moderetain information element.

Moreover, an identifier (e.g., a paging controller identifier (PCID), anauthenticator network entity ID, etc.) of a network entity, which keepsthe information retention-requested by the mobile station, can befurther included in the deregistration response message.

If the serving station rejects the DCR mode entry request made by themobile station, it is able to send the deregistration response messageto the mobile station in a manner of setting an action code of thederegistration response message to 0x09 that is a value that instructs arejection of a context retention of the mobile station.

Meanwhile, having received the deregistration response message from theserving base station, the mobile station is able to operate in the DCRmode [S205].

While the mobile station is operating in the DCR mode, the mobilestation and the base station basically do not perform any data exchangeincluding a paging procedure except a case that the mobile station makesa request for a network re-entry in the DCR mode or a request for anextension of a resource retention time.

Afterwards, the mobile station is able to send a ranging request messageto the base station to enter a normal mode from the DCR mode [S206].

In doing so, in order to indicate that the DCR mode operation isterminated, the mobile station is able to set a ranging purpose code ofthe ranging request message to a specific value. Values of the settableranging purpose codes are described with reference to Table 3 asfollows.

TABLE 3 Ranging Purpose The presence of this item in the messageindicates It shall be included when the AMS is Indication the followingAMS action: If Bit#0 is set attempting to perform reentry. HO, to 1, itindicates that the AMS is currently location update or DCR modeextension. attempting HO reentry, or, in combination with a PagingController ID, indicates that the MS is attempting network reentry fromidle mode to the BS. In this case, Bit#1 shall be 0. If Bit#1 is set to1, it indicates that the AMS is initiating the idle mode location updateprocess, or, in combination with CRID, it indicates that the AMS isinitiating DCR mode extension. In this case, Bit#0 shall be 0. If Bit#2is set to 1, ranging request for emergency call setup. When this bit isset to 1, it indicates AMS action of Emergency Call process. If Bit#4 isset to 1, it indicates that the AMS is attempting to perform locationupdate due to a need to update service flow management encodings forE-MBS flows. If Bit #5 is set to 1, it indicates that AMS is initiatinglocation update for transmission to DCR mode from idle mode. If Bit #6is set to 1 in combination with ID of the network entity thatassigns/retains the context, it indicates that the AMS is currentlyattempting reentry from DCR mode. If Bit#7 is set 1, it indicates thatthe AMS is currently attempting network reentry after experiencing acoverage loss. If Bit#8 is set to 1, it indicates that the AMS iscurrently attempting network reentry from a IEEE802.16e only Legacy BS

Referring to Table 3, the mobile station sets a ranging purpose field to0x06 that is the bit indicating a network re-entry in DCR mode. And, anidentifier of a network entity, which keeps the informationretention-requested by the mobile station, a DID (or CRID), a basestation identifier (BSID) at the time of the mobile station's entry atthe DCR mode and the like can be included in a ranging request messageby the mobile station.

Preferably, the transmission of the ranging request message is performedprior to expiration of a resource retain timer. The informationretention-requested by the mobile station is kept in the network entityuntil the expiration of the resource retain timer. This is because theDCR mode is terminated according to the expiration of the resourceretain timer. In consideration of this situation, the mobile station isable to attempt a network re-entry at any time until the expiration ofthe resource retain timer. If any action is not taken until thetermination of the DCR mode due to the expiration of the resource retaintimer, the mobile station may be able to perform an initial networkentry.

In order to extend the DCR mode before the expiration of the resourceretain timer, if a ranging request message, in which a correspondingranging purpose code is set, is sent to the base station, the resourceretain timer can be extended. In particular, the DCR mode can beextended in the following manner. First of all, by setting the rangingpurpose code to 1 and having a CRID included in a ranging requestmessage, the mobile station sends the ranging request message to thebase station.

Although the mobile station is described in the present embodiment asattempting the network re-entry at the serving base station at that timeof entering the DCR mode, the mobile station is able to attempt anetwork re-entry at another base station as well.

Accordingly, the serving base station is able to obtain information onthe mobile station kept by the corresponding network entity [S207].

The following steps including a step S208 are similar to those of anetwork re-entry procedure in a general idle mode. For clarity, detailsof the following steps next to the step S207 shall be omitted from thefollowing description.

Meanwhile, according to another example of the present embodiment, amobile station is able to enter a DCR mode from an idle mode. This isexplained with reference to FIG. 3 as follows.

FIG. 3 is a diagram of one example for an operational process for amobile station to enter a DCR mode from an idle mode according to oneembodiment of the present invention.

Referring to FIG. 3, assume that a mobile station operates in idle mode.And, assume that information on the mobile station is retained by apaging controller in case of an idle mode entry [S301].

The mobile station is able to receive a paging message according topaging information (e.g., a paging cycle, a paging offset, etc.)allocated when the idle mode was entered [S302].

In this case, the mobile station is able to perform a location update toenter a DCR mode from the idle mode. For this, the mobile station isable to send a ranging request (AAI_RNG-REQ) message to a serving basestation [S303].

In doing so, in order to indicate a DCR mode entry, the mobile stationpreferably sets a ranging purpose code of the ranging request message to0x05 indicating the DCR mode entry from the idle mode.

When a CRID is used as an identifier for identifying a mobile station inDCR mode, if a base station grants a DCR entry request made by themobile station, the mobile station starts to operate in the DCR modeafter the grant.

When a DID is used as an identifier for identifying a mobile station inDCR mode, if a base station grants a DCR entry request made by themobile station, the base station is able to update a DID of thecorresponding mobile station [S304]. In particular, a DID equal to ordifferent from the former DID allocated to the mobile station in theidle mode is allocated and paging information is not included or can beset to ‘0’ or ‘null’. If paging information is included in the DID, allbit corresponding to the paging information can be set to 0 and anidentifier of a network entity, which keeps information on the mobilestation, is usable for the update of DID. In case that a DCR mode mobilestation identifier different from a mobile station identifier receivedin case of the idle mode entry is allocated, the step S304 is notexecuted. And, a DCR mode mobile station identifier of a new type isdelivered by being included in a ranging response message. Thisidentifier of the new type is allocated irrespective of the paginginformation.

In order to inform the mobile station of the DCR mode grant, the basestation sends a ranging response (AAI_RNG-RSP) message in which anaction code of a location update response is set to 0x04 [S305].

Accordingly, the mobile station is able to operate in the DCR mode[S306, S307]. As the mobile station operates in the DCR mode, the mobilestation does not receive a paging message.

As the mobile station operates in the DCR mode, a network entity (e.g.,authenticator ASN GW), which keeps retention request information of themobile station, retains the corresponding information while a resourceretain timer is valid.

In this case, as mentioned in the foregoing description, the update ofDID is performed by each of the mobile station and the base station at adifferent timing point or the DID can be simultaneously updated by bothof the mobile station and the base station as soon as the DCR mode isinitiated. The DID updates of the mobile and base stations may beperformed to enable the mobile station, the base station and the networkto clearly recognize the switch to the DCR mode that does not require apaging procedure. The DID update can be implicitly performed by each ofthe mobile station and the base station according to a prescribed ruleor can be explicitly notified to the mobile station by the base stationvia the ranging response message.

In case that the base station rejects the DCR mode entry of the mobilestation, the base station is able to sent the ranging response messagein the step S305 to the mobile station in a manner of setting an actioncode of a location update response thereof to 0x05.

Meanwhile, according to a further example of the present embodiment, amethod for a mobile station to enter an idle mode from a DCR mode isprovided. This is described with reference to FIG. 4 as follows.

FIG. 4 is a diagram of one example for an operational process for amobile station to enter an idle mode from a DCR mode according to oneembodiment of the present invention.

Referring to FIG. 4, assume that a mobile station operates in a DCRmode. And, assume that information on the mobile station is retained bysuch a prescribed network entity as a paging controller, anauthenticator ASN-GW and the like [S401].

As the mobile station operates in the DCR mode, the mobile station doesnot receive a paging message [S402].

In order to enter an idle mode from the DCR mode, the mobile station isable to perform a location update. As a means for performing thelocation update, the mobile station is able to send a ranging request(AAI_RNG-REQ) message to a serving base station [S403].

In doing so, in order to indicate an idle mode entry request, it ispreferable that a ranging purpose code of the ranging request message isnewly defined.

When a base station grants the idle mode entry request made by themobile station, in case that a CRID is used as an identifier foridentifying the mobile station in the DCR mode, a DID for identifyingthe mobile station in the idle mode and information (e.g., a pagingcycle, a paging offset, a PCID, etc.) corresponding to paginginformation are included in a ranging response message and the basestation can send the ranging response message to allocate the DID andthe information. When a Did is used as an identifier for identifying themobile station in the DCR mode, in case that a previous DOD isidentically used in the idle mode, it is able to send a ranging responsemessage including information (e.g., a paging cycle, a paging offset, aPCID, etc.) corresponding to paging information only. In case that a DIDdifferent from the DID used in the DCR mode is used, it is able to senda ranging response message including a newly allocated DID andinformation (e.g., a paging cycle, a paging offset, a PCID, etc.)corresponding to paging information only.

Subsequently, the base station is able to send a ranging responsemessage as a location update response to the mobile station in responseof the location update [S405].

Preferably, a location update response code is set as the locationupdate response to a value, which indicates that the idle mode entryfrom the DCR mode is granted, in the sent ranging response message.Since the indicating value is not currently defined, the presentinvention proposes to modify the setting of the ranging response messageinto Table 4.

TABLE 4 Name (in AAI_RNG-RSP) Value Usage Location Update 0x00 = Successof Location Update It shall be included Response 0x01 = Failure ofLocation Update when an ABS sends an 0x02 = Reserved AAI_RNG-RSP message0x03 = Success of location update and DL in response to an trafficpending AAI_ RNG-REQ message 0x04 = Allow AMS's DCR mode request used toperform 0x05 = Reject AMS's DCR mode request location update 0x06 =Allow AMS's Idle mode request from DCR mode 0x07~0xFF: Reserved

Referring to Table 4, the base station is preferably set a locationupdate response code to 0x06 to grant the idle mode entry of the mobilestation.

Accordingly, the mobile station updates the DID and is then able tooperate in the idle mode [S406, S407]. Afterwards, the mobile station isable to receive a paging message forwarded to itself according to thepaging information.

Second Embodiment

According to another embodiment of the present invention, a method for amobile station to terminate a DCR mode and perform a network re-entry isprovided.

For this, the present embodiment proposes three kinds of methods forperforming a network re-entry.

First Method: Using a CRID and a ranging purpose indicator allocated viaa registration response message in case of a DCR mode entry or a networkentry, it is able to perform a network re-entry.

Second Method: Normal initial entry procedure can be performed.

Third Method: In case that a femto base station has a unified rangingchannel structure (i.e., like a macro bandwidth channel structure, ifboth a ranging preamble and a quick access message are transmittedtogether), it is able to indicate a network re-entry using a 1-bitindication of a bandwidth quick message. In this case, the 1-bitindication can be represented as a ranging purpose indicator. And, bandrequest size information (BR size: 2 bits) for sending a ranging requestmessage can be contained in a ranging preamble.

First of all, the first method is explained with reference to FIG. 5.

FIG. 5 is a diagram of one example for an operating process for a mobilestation operating in DCR mode to perform a network re-entry according toanother embodiment of the present invention.

Referring to FIG. 5, a mobile station in a state connected to a basestation can determine whether to enter a DCR mode [S501].

The mobile station sets a deregistration request code(Deregistration_Request_Code) of a deregistration request message to0x04 and is then able to send the deregistration request message to thebase station [S502].

Meanwhile, in response to the deregistration request message, the basestation is able to sent a deregistration response message including aresource retain timer information to the mobile station [S503].

In this case, an identifier (i.e., CRID) for identifying the mobilestation in the DCR mode is allocated to the mobile station via aregistration response (AAI_REG-RSP) message or is newly allocated via aderegistration response (AAI_DREG-RSP) message or a ranging response(AAI_RNG-RSP) message.

A network including the base station retains information on the mobilestation and manages a list indicating information on a mapping relationbetween the CRID allocated to the mobile station and a medium accesscontrol (MAC) address [S504].

Afterwards, the mobile station terminates the DCR mode and is then ableto transmit a ranging sequence (e.g., a CDMA ranging code) forattempting a network re-entry to the base station. In response to theranging sequence, the base station transmits a success or failure ofranging, a physical parameter correction value and the like to themobile station via a ranging response or ranging acknowledgement(AAI_RNG-ACK) message [S505, S506].

Accordingly, the mobile station sends a ranging request message to thebase station in a manner that a CRID and a cipher based messageauthentication code (CMAC Tuple) for authentication are included in theranging request message [S507].

In doing so, the mobile station is able to set a ranging purpose code to0x06 in the ranging request message.

Subsequently, in response to the ranging request message, the basestation sends a ranging response message to the mobile station in amanner that a station identifier (STID) or a temporary stationidentifier (T-STID) to be used for the base station by the mobilestation is included in the ranging response message [S508]. In doing so,if the CMAC Tuple transmitted by the mobile station is valid, the basestation ciphers the ranging request message and is then able to securelydeliver the STID to the mobile station. On the contrary, if the T-STIDis included, the base station is able to allocate the STID to the mobilestation via an unsolicited ranging response (unsolicited AAI_RNG-RSP)message in addition [not shown in the drawing].

Afterwards, the mobile station completes the network re-entry procedureand is then able to perform normal data exchange in a state connected tothe base station [S509].

In the following description, the second method is explained withreference to FIG. 6.

FIG. 6 is a diagram of another example for an operating process for amobile station operating in DCR mode to perform a network re-entryaccording to another embodiment of the present invention.

Referring to FIG. 6, as the steps shown in FIG. 6 are mostly similar tothose shown in FIG. 5, description of the redundant parts is omitted forclarity of this disclosure but the differences in-between are describedas follows.

First of all, in a step S603, a base station does not allocate a CRID toa mobile station. Therefore, in a step S604, a network including thebase station identifies the retained information of the mobile stationusing a MAC address of the mobile station only instead of information onmapping the CRID and the MAC address to each other.

In a step S607, the mobile station sends a ranging request message in amanner that its MAC address is included in the ranging request messageinstead of the CRID. Subsequently, the base station is able to receivethe corresponding information from a network entity, which keeps theinformation on the mobile station, using the MAC address of the mobilestation.

The third method is described as follows.

First of all, as mentioned in the foregoing description, the thirdmethod is applicable if a ranging channel structure of a base station isa unified ranging channel structure capable of transmitting a rangingpreamble and a quick access message together like a macro bandwidthchannel structure. One example for the unified ranging channel structureis shown in FIG. 7.

Thus, if the unified ranging channel is applied, the bandwidth quickaccess message can indicate that the mobile station is the mobilestation that attempts a network re-entry in a DCR mode using 1-bitindicator. Moreover, a size of a bandwidth (BR size) for transmitting aranging request message can be indicated via a ranging preamble using 2bits. In the following description, when a unified ranging channel issupported, a network re-entry procedure of a mobile station is describedwith reference to FIG. 8.

FIG. 8 is a diagram of a further example for an operating process for amobile station operating in DCR mode to perform a network re-entryaccording to another embodiment of the present invention.

Referring to FIG. 8, as steps S801 to S804 are similar to the formersteps S601 to S604 shown in FIG. 6, description of redundant parts isomitted from the following.

First of all, a mobile station is able to send a quick access message toa base station together with a ranging preamble (code) to perform anetwork re-entry from a DCR mode [S805].

In ding so, the mobile station is able to indicate a mobile station thatperforms a network re-entry from the DCR mode via a ranging purposeindication. Moreover, the mobile station is able to transmit a bandwidthsize (size including a MAC address and a CMAC) for a ranging request(AAI_RNG-REQ) message to transmit together with a preamble.

The rest of steps in FIG. 8 are similar to those in FIG. 6 and theirdescriptions are omitted from the following.

Third Embodiment

According to a further embodiment of the present invention, anidentifier (i.e., CRID) for identifying a mobile station in a DCR modeis allocated to be discriminated from a DID for identifying the mobilestation in an idle mode. Types of CRID for the discrimination areproposed as follows.

Type 1: Bit(s) Added to DID to Identify DCR Mode

Generally, CRID can be configured in a manner that 1 or 2 bits are addedto 10-bit MSB (most significant bits) or LSB (least significant bits) ofDID for identifying a mobile station in an idle mode.

If 1 bit is added, it is able to indicate whether this identifier isused in the DCR mode only. If 2 bits are added, it is able to alsoindicate whether the DCR mode is the mode for the purpose (e.g., powersaving (hibernation)) of the DCR mode or the mode for accessing anotherwireless system (inter-RAT).

Type 2: Paging Cycle and Paging Offset Included in Prescribed IdentifierBit

First of all, irrespective of DID, CRID can be configured in a mannerthat identifier bit of a prescribed length is combined with bit (e.g., 4bits) indicating a paging cycle and bit (e.g., 4 bits) indicating apaging offset.

In this case, if at least one of the paging cycle and the paging offsetis set to a specific value, it is able to indicate that it is applied toa DCR mode. If at least one of the paging cycle and the paging offset isset to a value different from the specific value, it is able to actuallyindicate a value of the paging cycle or the paging offset. Moreover, thepaging cycle bits and the paging offset bits can indicate whether to beapplied to the DCR mode in one body.

Type 3: Setting Paging Cycle Bits of DID Used for Idle Mode to SpecificValue

First of all, MSB 4 bits of DID used for idle mode indicate a pagingcycle. If theses bits indicating the paging cycle are set to a specificvalue e.g., 0x0000), this can be used as a CRID for identifying DCR-modemobile station. In particular, the DID having the MSB set to a specificvalue can be allocated as the CRID to the mobile station in the DCR modeonly.

Type 4: Identifier Bits of Network Entity, which Retains ContextInformation of MS, to DID

First of all, CRID can be configured in a manner that at least one ofbits of an identifier (e.g., authenticator ASN-GW) of a network entity,which retains context information of DCR-mode mobile station, is addedto 10-bit MSB or LSB of DID.

Besides, the above described configuration of the CRID according to thepresent embodiment is applicable to the aforesaid first and secondembodiments.

Structures of Mobile Station and Base Station

In the following description, a mobile station and base stations (FBS,MBS) according to another embodiment of the present invention forimplementing the above described embodiments of the present inventionare explained.

First of all, a mobile station works as a transmitter in uplink and isable to work as a receiver in downlink. A base station works as areceiver in uplink and is able to work as a transmitter in downlink. Inparticular, each of the mobile station and the base station can includea transmitter and a receiver for transmission of information and/ordata.

Each of the transmitter and the receiver can include a processor, amodule, a part and/pr a means for performing embodiments of the presentinvention. In particular, each of the transmitter and the receiver caninclude a module (means) for encrypting a message, a module forinterpreting the encrypted message, an antenna for transceiving themessage and the like. Examples of these transmitting and receiving sidesare explained with reference to FIG. 9 as follows.

FIG. 9 is a block diagram for an example of a transmitting and receivingside structure according to another further embodiment of the presentinvention.

Referring to FIG. 9, a left side shows a structure of a transmittingside and a right side shows a structure of a receiving side. Thetransmitting/receiving side can include an antenna 5/10, a processor20/30, a transmitting (Tx) module 40/50, a receiving (Rx) module 60/70and a memory 80/90. Each of the elements can perform a correspondingfunction. The respective elements are explained in detail as follows.

First of all, the antenna 5/10 performs a function of transmitting asignal generated by the Tx module 40/50 externally or a function ofreceiving a radio signal externally and then delivering the receivedradio signal to the Rx module 60/70. If MIMO function is supported, atleast two antennas can be provided.

The antenna, Tx module and Rx module can configure a radio communication(RF) module.

The processor 20/30 controls overall operations of the transmitting orreceiving side in general. For instance, the processor 20/30 can performa controller function for performing the above described embodiments ofthe present invention, a MAC (medium access control) frame variablecontrol function, a handover function, an authentication function, anencryption function and the like.

In particular, a processor of a mobile station can determine whether toenter a DCR mode. In case of determining to enter the DCR mode, theprocessor is able to control the wireless communication module to send aderegistration request message to a base station. In doing so, theprocessor determines information to be retained by a network entity andis then able to set parameters associated with the corresponding messageand is also able to set a request code of the corresponding message to0x04. The processor of the mobile station controls the wirelesscommunication module to receive a deregistration response message fromthe base station. The processor checks an action code value of thereceived message and is then able to determine whether to grant the DCRmode entry request.

In the course of operating in an idle mode, the processor of the mobilestation is able to control a ranging request message, in which a rangingpurpose code is set to 0x05 to enter a DCR mode, to be sent to the basestation.

Afterwards, the processor of the mobile station can control overallfunctions of the mobile station to operate to cope with the DCR mode.The processor is also able to determine whether to re-enter a network.In case of determining to re-enter the network, the processor is able tocontrol a location update procedure to be executed. For this, theprocessor controls the wireless communication module to send a rangingrequest message to the base station. In doing so, the processor sets aranging purpose code to 0x06 in the ranging request message and thenenables CRID to be included therein.

In this case, the CRID can be allocated via a registration response(AAI_REG-RSP) message in case of an initial network entry of the mobilestation or can be updated via a deregistration response (AAI_DREG-RSP)message or a ranging response (AAI_RNG-RSP) message.

Besides, the processor of the mobile station is able to control overalloperations of the operating processes disclosed in the above describedembodiments.

The Tx module 40/50 performs prescribed coding and modulation on data,which is scheduled to be externally transmitted by the processor 20/30,and is then able to deliver the coded and modulated data to the antenna10/5.

The Rx module 60/70 reconstructs a radio signal externally received viathe antenna 5/10 into original data by performing decoding anddemodulation on the radio signal and is then able to deliver thereconstructed original data to the processor 20/30.

A program for processing and control of the processor 20/30 can bestored in the memory 80/90. And, the memory 20/30 can perform a functionfor temporary storage of inputted/outputted data. Moreover, the memory80/90 can include at least one storage medium of such a type as a flashmemory type, a hard disk type, a multimedia card micro type, a card typeof memory (e.g., SD memory, XD memory, etc.), a Random Access Memory(RAM) type, an SRAM (Static Random Access Memory type), a Read-OnlyMemory (ROM) type, an EEPROM (Electrically Erasable ProgrammableRead-Only Memory) type, a PROM (Programmable Read-Only Memory) type, amagnetic memory type, a magnetic disc type, and optical disc type, andthe like.

Meanwhile, a base station uses at least one of the above mentionedmodules to perform a controller function for performing theabove-described embodiments of the present invention, an OFDMA(orthogonal frequency division multiple access) packet scheduling, TDD(time division duplex) packet scheduling and channel multiplexingfunction, a MAC (medium access control) frame variable control functionaccording to a service characteristic and electric wave environment, afast traffic real-time control function, a handover function, anauthentication and encryption function, a packet modulation/demodulationfunction for data transmission, a fast packet channel coding function, areal-time modem control function and the like or can further includeseparate means, modules and/or parts for performing these functions.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents. Moreover, claimsfailing to be explicitly cited in-between are combined to construct newembodiments or can be included as new claims by Amendment after filingthe application.

What is claimed is:
 1. A method of a DCR (deregistration with contentretention) mode operation of an AMS (advanced mobile station) in abroadband wireless access system, the method comprising: transmitting afirst message including a first code indicating a DCR mode entry requestto a base station; receiving a second message including a second codeindicating whether to allow the entry request from the base station; ifthe second code is set to a value indicating an allowance of the entryrequest, operating in the DCR mode while a preset timer is valid; andtransmitting a third message for a DCR mode extension to the basestation, before the preset timer expires.
 2. The method of claim 1,further comprising transmitting a registration request (AAI_REG-REQ)message to the base station; and receiving a registration response(AAI_REG-RSP) message from the base station, wherein the registrationresponse message includes an identifier for identifying the AMS inassociation with connection information (AMS context) of the AMS in anetwork including the base station.
 3. The method of claim 2, whereinthe third message includes the identifier and a third code indicatingthe DCR mode extension.
 4. The method of claim 2, further comprising:receiving, from the base station, a fourth message in response to thethird message; and extending the preset timer.
 5. The method of claim 2,wherein the first message is a deregistration request (AAI_DREG-REQ)message, wherein the second message is a deregistration response(AAI_DREG-RSP) message, wherein the third message is a ranging requestmessage (AAI-RNG-REQ), and wherein the identifier is a context retentionidentifier (CRID).
 6. The method of claim 2, further comprising:transmitting, to the base station, a fifth message for a network reentryfrom the DCR mode before the preset timer expires; and performingnetwork reentry to the base station, wherein the fifth message includesthe identifier and a fourth code indicating the network reentry from theDCR mode.
 7. A method of a DCR (deregistration with content retention)mode operation of a base station in a broadband wireless access system,the method comprising: receiving a first message including a first codeindicating a DCR mode entry request from an advanced mobile station(AMS); determining whether to allow the entry request; when the entryrequest is allowed, delivering a context of the AMS to a prescribednetwork entity; transmitting a second message including a second codeindicating an allowance of the entry request to the AMS; and receiving athird message for a DCR mode extension from the AMS, before a presettimer expires.
 8. The method of claim 7, further comprising: receiving aregistration request (AAI_REG-REQ) message from the AMS; andtransmitting a registration response (AAI_REG-RSP) message including anidentifier for identifying the AMS in association with the context ofthe AMS in a network including the base station to the AMS.
 9. Themethod of claim 8, wherein the third message includes the identifier anda third code indicating the DCR mode extension.
 10. The method of claim8, further comprising: transmitting, to the AMS, a fourth message inresponse to the third message; and extending the preset timer.
 11. Themethod of claim 8, wherein the first message is a deregistration request(AAI_DREG-REQ) message, wherein the second message is a deregistrationresponse (AAI_DREG-RSP) message, wherein the third message is a rangingrequest message (AAI-RNG-REQ), and wherein the identifier is a contextretention identifier (CRID).
 12. The method of claim 8, furthercomprising: receiving, from the AMS, a fifth message for a networkreentry from the DCR mode before the preset timer expires; and allowingnetwork reentry of the AMS, wherein the fifth message includes theidentifier and a fourth code indicating the network reentry from the DCRmode.
 13. A mobile station which operates in a broadband wireless accesssystem, the mobile station comprising: a processor; and a radiocommunication (RF) module configured to transceive a radio signalexternally under the control of the processor, wherein the processor isconfigured to transmit a first message including a first code indicatinga DCR mode entry request to a base station, to receive a second messageincluding a second code indicating whether to allow the entry requestfrom the base station, to operate in the DCR mode while a preset timeris valid if the second code is set to a value indicating an allowance ofthe entry request, and to transmit a third message for a DCR modeextension to the base station, before the preset timer expires.
 14. Themobile station of claim 13, wherein the processor is further configuredto: transmit a registration request (AAI_REG-REQ) message to the basestation; and receive a registration response (AAI_REG-RSP) message fromthe base station, wherein the registration response message includes anidentifier for identifying the mobile station in association withconnection information (context) of the mobile station in a networkincluding the base station.
 15. The mobile station of claim 14, whereinthe third message includes the identifier and a third code indicatingthe DCR mode extension.
 16. The mobile station of claim 14, wherein theprocessor is further configured to: receive, from the base station, afourth message in response to the third message; and extend the presettimer.
 17. The mobile station of claim 14, wherein the first message isa deregistration request (AAI_DREG-REQ) message, wherein the secondmessage is a deregistration response (AAI_DREG-RSP) message, wherein thethird message is a ranging request message (AAI-RNG-REQ), and whereinthe identifier is a context retention identifier (CRID).
 18. The mobilestation of claim 14, wherein the processor is further configured to:transmit, to the base station, a fifth message for a network reentryfrom the DCR mode before the preset timer expires; and perform networkreentry to the base station, wherein the fifth message includes theidentifier and a fourth code indicating the network reentry from the DCRmode.